1. Field of the Invention
The invention relates in general to a backlight module, and more particularly to a backlight module with a flexible printed circuit board which is bent to be disposed on a frame.
2. Description of the Related Art
Along with the progress in display technology, a backlight module is used in a liquid crystal display device to be a light source. The small-sized backlight module includes a light emitting diode (LED), a flexible printed circuit board, a frame and a light guide plate. The light guide plate is disposed in the frame. Referring to FIG. 1A, a sectional view of a flexible printed circuit board disposed at a frame is shown. The flexible printed circuit board 90 is bent to be disposed on two opposite sides of the frame 11, and glue 20 is smeared between the flexible printed circuit board 90 and the frame 11 to adhere the flexible printed circuit board 90 on the frame 11. The LED 70 is positioned at a side of the light guide plate 50. When the LED 70 emits light, the light will radiate into the light guide plate 50. The structure of the light guide plate 50 changes the direction of the light.
As the flexible printed circuit board 90 is bent to be disposed on the frame 11, the flexible printed circuit board 90 has bounceback stresses. Referring to FIG. 1B, the flexible printed circuit board in FIG. 1A rising up due to the bounceback is shown. After the flexible printed circuit board 90 rises up, the position of the LED 70 changes accordingly. Thus, a part of light emitted by the LED 70 can not radiate into the light guide plate 50, so that the light emitting efficiency of the backlight module 10 is reduced. Even the light uniformity of the backlight module 10 is reduced when the optical path of the light emitted by the LED 70 deflects.
A common method to resolve the above problem is to make the flexible printed circuit board 90 more firmly adhered on the frame 11 by the glue 20 with high adhesiveness. However, the smeared area for the glue 20 is limited and the use of the glue 20 with higher adhesiveness always further increases the cost. Another common method is to add a fixing member to avoid the bounceback of the flexible printed circuit board 90. For example, a frame (not illustrated) is added outside the flexible printed circuit board 90 to fix the flexible printed circuit board 90. Or, a clip (not illustrated) is temporarily used to clamp and fix the flexible printed circuit board 90 on the frame 11. However, adding an additional fixing member will increase both manufacturing cost and time. Furthermore, if the fixing member (the frame) is disposed outside the flexible printed circuit board 90, the overall thickness of the backlight module 10 increases as well. Therefore, how to reduce the occurrence of the bounceback of the bent flexible printed circuit board so as to avoid the light emitting efficiency and uniformity of the backlight module being affected caused by the deflection of the light source has become an imminent issue to be resolved.